The present invention relates to an image forming apparatus that employs an electrophotography.
A conventional electrophotographic image-forming apparatus includes a photoconductive drum. Disposed around the photoconductive drum are a charging section, an exposing section, a developing section, a transferring section and a cleaning section. The aforementioned structural elements are housed in a cartridge case.
The developing section includes primarily a developing roller and a developing blade. The developing blade extends in a direction parallel to the developing roller such that one of the long sides of the blade is in contact with the developing roller. The developing blade presses the toner against the circumferential surface of the developing roller so as to form a thin layer of toner on the developing roller. Then, the toner on the developing roller is brought into contact with the surface of the photoconductive drum as the developing roller rotates, so that the toner migrates from the developing roller to an electrostatic latent image formed on the drum. In this manner, the electrostatic latent image is developed into a toner image.
The image forming apparatus operates in two modes: a normal mode where an image is printed on ordinary paper and a thick paper/OHP mode where an image is printed on thick paper or a transparency that requires a longer fixing time than ordinary paper. Thus, the respective rollers are rotated at lower speeds in the thick paper/OHP mode than in the normal mode. In the normal mode, the printing speed is such that 12 pages of A4 size paper can be printed in a minute. In the thick paper/OHP mode, the printing speed is such that 5 pages of A4 size paper can be printed in a minute.
Thus, the rollers rotate at lower speeds in the thick paper/OHP mode than in the normal mode. Rotation at such low speeds can cause toner to be clumped between the developing blade and the developing roller. Toner clumping prevents a uniform layer of fresh toner from being formed on the developing roller, creating surface areas of the developing roller that has not a sufficient amount of toner deposited. This implies that portions of the electrostatic latent image corresponding to such areas are not properly developed into a toner image. As a result, the printed image has areas referred to as xe2x80x9cwhite linesxe2x80x9d in which no toner is deposited.
The present invention was made in view of the aforementioned
An image-forming apparatus includes a developing roller and a developing blade. The developing roller rotates in contact with a photoconductive drum to deposit toner to an electrostatic latent image formed on the photoconductive drum. The developing blade applies toner to the developing roller to form a thin layer of toner on the developing roller. The image-forming apparatus performs a printing operation that includes a paper-feeding period (first period) and a developing period (second period) following the paper-feeding period. The developing roller rotates relative to the toner-applying member at a first circumferential speed during the paper-feeding period, and then rotates at a second circumferential speed during the developing period, the second speed being lower than the first circumferential speed.
The paper-feeding period is a length of time during which a print medium is fed from a medium-holding cassette to a predetermined position in the image-forming apparatus.
The developing roller rotates at a circumferential speed between 73 mm/s and 1015 mm/s.
The developing roller may be rotated at a first circumferential speed until a circumferential surface of the developing roller as traveled over a first circumferential distance with respect to the developing blade. Then, the developing roller may be rotated relative to the developing blade at a second circumferential speed over a second circumferential distance when the surface has traveled over the first circumferential distance, the second circumferential speed being higher than the first circumferential speed. The second distance is longer than half a nip formed between said developing roller and developing blade.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.